Generally, when nonmetallic inclusions among molten steel are not removed between a steel-making process and a continuous casting process but remain on a thin sheet, it may cause scabs for large inclusions or sliver scabs on steel sheets. In case of wire rod steel sheet, this may be a cause for disconnection. In case of stainless steel sheets, however, if the nonmetallic inclusions remain on the steel sheet, there may be problems in terms of corrosion resistance. Therefore, the quality of the final product may be negatively affected.
Also, to decarbonize molten steel, oxyfuel gas may be blown into molten steel at various facilities (revolving furnace, RH, AOD, VOD). After decarbonization reaches the target concentration, molten steel has high oxygen concentration. Accordingly, deoxidizer is added to reduce such oxygen concentration, and generally, alloy or pure substance which uses Al, Si, MN, and the like, as main ingredients is used. However, when alumina (Al2O3), silica (SiO2) or a deoxidizer is combined/added for a deoxy product, a complex oxide may exist among molten steel. Meanwhile, when steel is taken out from AOD smelting furnace, inclusions on slag may exist on molten steel because the steel is taken out at the same time as the slag, and for the inclusions on the slag, spinell inclusions of high melting point may be extracted due to temperature drop.
Accordingly, it is necessary to minimize the adverse influence that is made on the qualities of the final products by prohibiting inclusions from being formed or removing inclusions formed, from a steel-making process, which is a process before solidification of molten steel is completed, to a continuous casting process.
To overcome the aforementioned problem, the purpose of the present invention that is contrived is to provide a method for manufacturing high cleanliness molten steel by suppressing inclusions from being formed or removing inclusions formed from a steel-making process to a continuous casting process.
Also, another purpose of the present invention is to provide a refining device for manufacturing high cleanliness molten steel.